1. Technical Field
The invention relates to automated monitoring and control of a drilling operation carried out in a borehole.
2. Description of Related Art
Rate of penetration (ROP) of a drilling process is the speed at which a bit drills through a subsurface formation to increase the reach of a borehole in the subsurface formation during the drilling process. Automated drilling based on optimizing ROP is known in the art. For example, U.S. Pat. No. 6,026,912 (King et al.; 22 Feb. 2000) describes a method and system for optimizing ROP in drilling operations. In the King et al. patent, an optimum weight-on-bit (WOB) necessary to achieve an optimum ROP is continuously determined, and weight is maintained on the bit at the optimum WOB during drilling.
Mechanical specific energy (MSE) of a drilling process is a measure of the efficiency of the drilling process. Automated drilling based on optimizing MSE is known in the art. For example, U.S. Patent Application Publication No. 2008/0156531 (Boone et al., 3 Jul. 2008) describes methods and apparatus for automated drilling based on MSE. In the Boone et al. publication, the methods include sequentially varying WOB and bit rotational speed (RPM) to find a desired MSE. Desirability of an MSE is based on comparing the MSE to a baseline MSE. If the MSE is substantially equal to or less than the baseline MSE, then the MSE is desirable relative to the baseline MSE. U.S. Patent Application Publication No. 2006/0162962 (Koederitz et al.; 27 Jul. 2006) describes monitoring MSE during drilling and using the MSE to detect onset of abnormal events during drilling.